#include <iostream>
#include <cmath>

using namespace std;

class Line
{
    double x1, y1, x2, y2;

public:

    Line(double x1=0, double y1=0, double x2=0, double y2=0)
        : x1(x1), y1(y1), x2(x2), y2(y2) {}

    double length()
    {
        return sqrt(pow(x2-x1, 2) + pow(y2-y1, 2));
    }
};

int main()
{
    Line line(0, 0, 3, 4);
    cout << line.length() << endl;
    return 0;
}